What causes slow acceleration in your car?

Here are 28 reasons that your car, van or truck could be accelerating more slowly than you expect.

1. Carrying weight – the impact of several passengers plus luggage will definitely be felt, particularly if you have a small engine with low torque. Try removing unnecessary items from the boot to get better acceleration and better fuel economy.
2. Headwinds – a strong headwind will push back fiercely against a vehicle with a high coefficient of drag (like most SUVs, vans, trucks and those towing a boxy trailer); sleek, powerful cars won’t notice much difference
3. Gradients – don’t underestimate the effect of gravity to slow you down. Accelerating uphill means you’re fighting against gravity trying to pull you back downhill
4. Surface traction – electronic stability control and traction control will cut the power output to the wheels if they need to stop the wheels spinning or breaking traction. This will slow your progress. It can be caused by loose or slippery surfaces or bald tyres
5. Poor quality fuel – if the fuel doesn’t have sufficient quality for your engine to unleash all its horsepower, your top-end acceleration will suffer. You might experience ‘pinking’ when using heavy acceleration
6. Larger wheels – if you put larger or heavier wheels on your vehicle, there’s more mass to get rotating. It’ll be subtle, but definitely will be there. Conversely, putting smaller wheels on your vehicle will improve acceleration
7. Roof rack – this will add much more air resistance and the effect is magnified at higher speeds
8. Altitude – internal combustion engines need air as part of creating power. There’s less oxygen at higher altitudes and this will rob you of kilowatts (just ask anyone that races the Pikes Peak Hillclimb)
9. Clogged or dirty fuel filter – if you haven’t changed it in a while then it could be full of debris because it’s been doing its job. It’s a simple mechanical fix
10. Hose leaks or blockages – turbo cars need to build up boost to get the most power. If there’s a leak, then boost pressure can’t build fully and you’ll lose power. All cars have a plethora of other hoses performing a variety of functions, and these degrade over time
11. It’s hot – air is less dense when it’s hot, so the pistons can’t pack as much into the cylinder before igniting the fuel. This means the explosion isn’t as effective as it could be
12. Mass air flow sensor is clogged or malfunctioning – this is located and attached to the inlet air cleaner and it measures how much air is flowing into the air intake. If the sensor is giving a false reading, the engine ECU won’t be able to calculate the correct air/fuel ratio
13. Wrong gear – the higher the gear, the slower the acceleration
14. Wrong mode – some cars have ‘comfort’, ‘economy’ or ‘snow’ mode which restricts power to the wheels
15. Throttle position sensor is malfunctioning – the accelerator pedal changes the opening angle of the throttle valve. This sensor detects the angle and sends the information to the ECU
16. Seat position – are you pushing the pedal to the floor? If you can’t reach the floor, move your seat forward. If you still can’t, is there something stuck under the gas pedal?
17. Clogged air filter – if the engine can’t breathe, you won’t get the maximum power output
18. Timing belt – a misaligned timing belt will cause the engine’s intake and exhaust valves to open out of sync
19. Spark plugs – the spark has to happen at precisely the right time, otherwise you get a misfire. Are the spark plugs in good condition?
20. Slipping clutch – if your clutch is wearing out, you might notice the engine racing when you press the accelerator, but the car doesn’t pick up speed quickly.
21. Handbrake/emergency brake is engaged – you’ll eventually notice the acrid smell of burning brake pads and then they’ll probably catch fire, but up until that point, your acceleration won’t be as good as it could be
22. Clogged fuel injectors – if the fuel isn’t atomised efficiently, power will drop
23. Fuel pump malfunction – if the pump isn’t providing enough fuel, you’ll need to replace it
24. Clogged catalytic converter – this causes too much back pressure on the engine. It can also catch fire
25. Engine is in limp mode – certain miscellaneous issues can trigger various levels of limp mode which electronically reduces the power until you get it repaired. You’ll notice this if you have a ‘check engine’ light and it’s yellow; red means you need to stop and sort it out immediately.
26. Other sensors – the ECU takes information from all kinds of sensors such as the MAP sensor, coolant temperature sensor, crankshaft sensor and camshaft sensor. If they’re not feeding the right information, engine performance will be compromised
27. Issues with the block – these issues tend to result in low compression and are caused by carbon build-up, worn cylinder linings, worn or cracked piston rings, worn valve springs, worn valves or a blown head gasket.
28. Low tyre pressure – if your tyres are underinflated, rolling resistances will be increased (it takes more effort to turn the wheels). Bear in mind that low temperatures will lower tyre pressures, too.